1. Field of the Invention
The present invention relates to an image forming device and a method for producing it. Specifically, the invention relates to an image forming device applicable for example to an original document reader in a facsimile device or in an image scanner, to an image reader used in an optical printer or the like, and to a light source for a self-scanning type printer.
2. Description of the Related Art
An example of conventional techniques related to the present invention is described for example in Japanese Examined Patent Publication No. 61-2929. The example as described is explained in the following with the drawings as attached to the publication.
FIGS. 24A-24C are drawings to show a structure of the conventional roof mirror lens array (RMLA), in which FIG. 24A is a plan view thereof, FIG. 24B an elevational view thereof, and FIG. 24C a drawing to show an example of integral formation of prisms and lenses. In the drawings, reference numeral 10 designates a prism lens array, 11 a prism array, 12 a lens array, 13 an object, and 14 an inverted equal-size image.
Integrally formed of a plastic are the lens array (LA) 12 having a plurality of lenses continuously formed and the roof prism array (RPA) 11 having a plurality of roof prisms continuously formed at the same arrangement pitch as that of the lens array and each roof prism having a rectangular reflection plane.
An erecting real image is formed in the arrangement direction (Y direction) of the lens array (LA) 12 and the roof prism array (RPA) 10 and in the orthogonal direction thereto (X direction). Specifically, since an erecting equal-size image is formed in the Y direction, an image obtained through a single pair of the lens array (LA) 12 and the roof prism array (RPA) is overlapped on images through other pairs in the Y direction to cover a necessary width.
An opening shape of each lens is properly determined to make a light amount distribution even in the Y direction, whereby the light amount distribution may be optimized.
As described, the image forming device as described in Japanese Examined Patent Publication No. 61-2929 is integrally formed of a plastic material with the lens array having numerous small lenses aligned on a line and with the roof prism array having numerous rectangular prisms aligned behind the small lenses in such a state that each edge line of the rectangular reflection plane is made correspondent with a curvature center of each small lens. The image forming device has such a drawback, as shown in FIG. 24A, that light from a region having a large angle of view in the arrangement direction of the roof prism lens array (RPLA) is reflected only by a single plane of the reflection plane of the roof prism array (RPA) and reaches an image plane without forming an erecting image.
Further, since the edge line of the rectangular reflection plane is coincident with the curvature center of the small lens, there is another drawback that a degree of freedom is restricted to select the angle of view thereby to force a restriction on the properties such as the light amount distribution and the resolving power.
It is proposed as shown in FIGS. 25 to 27 to improve the light amount distribution by providing a light shielding mask 15 to limit the opening shape of the lenses in front of the lens array. However, in order to shield the light reflected only by a single plane of the reflection plane of the roof prism array (RPA), the opening shape of the mask must be extremely reduced or the lenses must be discretely disposed, which inevitably decreases the light utilization efficiency.
An "optical image forming device" as described in Japanese Unexamined Patent Publication No. 56-149002 is composed of an elongate prism lens array in which a plate prism array 23 having a plurality of prisms is coupled with a plate lens array 25 having a plurality of lenses. In detail, a plate light shielding member 27 is provided between the lens array 25 and the prism array 23 while defining an opening 26 for each lens element in the optical image forming device. However, since the lens array is superimposed on the prism array in the direction of the optical axis, an optical axis offset is likely to occur due to machining errors, which results in degrading the imaging power.